74 BACTERIAL METABOLISM 



duced in the intestinal tract from tryptophan (an amino-acid found 

 in protein), chiefly by B. coli and B. proteus. The reactions through 

 which tryptophan is changed to indol by these organisms are as 

 follows. 1 



CH 2 .CHNH 2 .COOH / \ _ CH 2 .CH 2 .COOH 



+ H 2 = + NHs Indol propionic acid 



+30= 



NH \X NH 



Tryptophan. (deaminization) 



. Indol propionic acid. 



/\ /\ 

 \ CH 2 .COOH 



CO 2 + H 2 O- 



Skatol + 3 O 

 NH 

 Indol acetic acid. Skatol. 



C0 2 + H 2 



NH 



Indol. 



Indol contains little or no energy for most bacteria, and it is left 

 as such in the culture medium or the intestinal tract. Indol is fre- 

 quently absorbed from the intestinal tract, but it has little or no 

 energy for the human body it is oxidized in the liver to indoxyl 



X\ 



OH 



and is excreted and appears 



in the urine as indican 

 "NH 



B. coli, B. proteus, and other organisms which "form indol" utilize 

 the alanin radical of the tryptophan molecule (alpha amino propionic 

 acid) for energy, first eliminating the nitrogen (deaminization), then 

 oxidizing the carbon. The indol radical which is left is not a source 

 of energy; it can not be oxidized by these organisms, consequently 

 it remains as such in culture media or is absorbed from the intestinal 

 tract. 



1 Nencki, Sitzungsber. Wien. Akad., 1898, II Abt., xcviii, 412. 



